The subject matter disclosed herein relates to premixed direct injection nozzles and more particularly to a direct injection nozzle having better mixing that includes a cooling system to provide resistance to thermal damage.
The primary air polluting emissions usually produced by gas turbines burning conventional hydrocarbon fuels are oxides of nitrogen, carbon monoxide, and unburned hydrocarbons. It is well known in the art that oxidation of molecular nitrogen in air breathing engines is highly dependent upon the maximum hot gas temperature in the combustion system reaction zone. One method of controlling the temperature of the reaction zone of a heat engine combustor below the level at which thermal NOx is formed is to premix fuel and air to a lean mixture prior to combustion
There are several problems associated with dry low emissions combustors operating with lean premixing of fuel and air. That is, flammable mixtures of fuel and air exist within the premixing section of the combustor, which is external to the reaction zone of the combustor. Typically, there is some bulk burner tube velocity, above which a flame in the premixer will be pushed out to a primary burning zone. There is a tendency for combustion to occur within the premixing section due to flashback, which occurs when flame propagates from the combustor reaction zone into the premixing section, or auto ignition, which occurs when the dwell time and temperature for the fuel/air mixture in the premixing section are sufficient for combustion to be initiated without an igniter. The consequences of combustion in the premixing section, and the resultant burn in the nozzle, are degradation of emissions performance and/or overheating and damage to the premixing section.
With natural gas as the fuel, premixers with adequate flame holding margin may usually be designed with reasonably low air-side pressure drop. However, with more reactive fuels, such as high hydrogen fuel, designing for flame holding margin and target pressure drop becomes a challenge. Since the design point of state-of-the-art nozzles is about 3000 degrees Fahrenheit flame temperature, flashback into the nozzle can cause damage to the nozzle in a very short period of time.